Transcript Document
2003 UB313: The 10th Planet? Extra-Solar or Exoplanets • Planets around stars other than the Sun • Difficult to observe • Hundreds discovered (> 2000 so far) Circa 2013, Courtesy Kepler: Billions!! • Jupiter to Earth sizes • Surprise: Some stars with Jupiter mass planets within 1 AU (revised theory of planet formation ?) • Habitable Zone: Distance out to where water is liquid Extra-solar planets around distant stars First image of an exoplanet Transiting Hot Saturn with a large dense core Astronomers have found a weird new creature: a planet whose core holds 65 Earths' worth of heavy rocky stuff. Saturn-mass planet transiting across its star Discovering Planets with Life Sunlight is reflected off the Earth, hits the Moon and bounces back to Earth Earthshine is seen in the faint glow our world gives to dark areas of the Moon The light carries information about Earth's atmosphere and surface properties Scientists see details in the light that betray different gases, even vegetation The knowledge can be applied to the search for distant worlds Detect the presence of atoms/molecules that make up vegetation or life 7.5 Earth-mass planet Found: 3 'Neptunes' and a 'hot Jupiter' 600 LY’s from the Earth, the planetary system is in the habitable zone with conditions enabling liquid water to exist HD 188753 b - A planet in a triple star system 5.9 Earth mass planet in Gliese 876 system The Search for New Planets Techniques for discovering exoplanets • • • • • Direct observation few Protoplanetary disks Many seen Doppler Effect Absorption red/blue shift Transit across the star Dimming starlight KEPLER spacecraft Transiting planet with 1/10,000 variation in starlight • Gravitational Microlensing few • “Free-floating” planets, unattached to stars About 3 times the mass of Jupiter – orbit predicted (!) from structure of ring. 870 year orbit. Orbits around the Centre of Mass Doppler Effect • Star’s spectral absorption lines shift towards the blue when the wobble moves the star towards the Earth. • Star’s spectrum shifts towards the red when the wobble moves the star away from the Earth. • Measuring the orbital motions provides an estimate of the unseen planet’s mass. P Star’s spectrum Doppler shifts blueward S To the observer S Star’s spectrum Doppler shifts redward P Planetary Transit planetary transit in the star HD 209458 Planetary Data •The planetary transit and Doppler data combined gives us more information: •The orbital tilt: i=86.68° ± 0.14° •The planet's mass: M=0.69 ± 0.05 MJup •The planet’s radius: R=1.347 ± 0.050 RJup •The planet's mean density: 350 kg/m3 •It is a giant gas planet intermediate in mass between Jupiter & Saturn. Kepler Transits Detection •July 2015 •1211 planets in 680 planetary systems / 358 multiple planet systems •Thousands of candidates from Kepler spacecraft – statistical studies say almost all of these planets will be real… The Challenges – Transit Depth The depth of the transit is set by how much of the star is covered by the planet – the fractional change is (radius of planet/radius of star)2~104 for the Earth ~102 Jupiter To look for the small dips associated with Earth almost certainly requires doing it from space in order to get the necessary stability Kepler Launched in 2009 – in theory capable of detecting transiting Earths It stares at one patch of sky and monitors the brightnesses of about 100,000 stars looking for transits Gravitational Microlensing Gravity’s Telescope S. Gaudi Gravity bends light rays, and so a foreground star can focus the light of a more distant star onto the observer Current Total (exoplanets.eu) Confirmed planets (as of July 2015) 1935 planets around 1225 stars, 484 multiple planet systems Plus : Kepler “candidates” (4696 !) N.B. • RV – Radial Velocity Doppler Effect • Transits – Only few from the ground Most from space via Kepler satellie • Snow line: gases/ices condense Gaudi Breaking news : NASA/Kepler confirms finding Earth-like planet around Solar type star in habitable Zone (July 23, 2015) !! Earth’s bigger, older cousin ? Kepler 452-b Host star : G2, 6 billion years old 20% brighter, 10% larger diameter Planet : 1.6x Earth radius, a =1.05 AU, P=385 Mass ? Composition ?